One transmission route using normal-conducting cables is composed of a plurality of circuits to accommodate a failure (e.g. Non-Patent Document 1). For example, one route may be composed of three circuits, where the maximum transmission capacity provided by all of the circuits may be 3E, with the maximum capacity of each cable circuit being 1.5E such that in the case of one circuit becoming unavailable due to a failure, the remaining two circuits are still capable of providing the transmission capacity of 3E.
Basically, when the power demand in a geographical area is expected to increase, transmission of electric power matching the increased demand can be only achieved by installation of an additional cable.
Non-patent Document 1: IIZUKA, Kihachiro, “Power Cable Technology Handbook, New Edition”, Denkishoin Co., Ltd., Mar. 25, 1989, first edition, pp. 14-17